This is a totally pointless discussion, imho. But for what it's worth, I'll add to the conjecture pool that it may well be that retailers indicate they are not interested in selling the 20gb version, and highly prefer having only one SKU (very understandable). Perhaps Sony will reconsider this by focussing 100% on getting one SKU out there and getting that single SKU to the lowest possible manufacturing / price point. I don't know. It could make sense - always include Wifi if you can get the price for internal Wifi low enough (should be really cheap by now?) and upscale the HDD according to market developments (when, say, 60GB costs the same or less as 20GB, pick 60GB).
People can ebay-off the 60GB HDDs if needs be, and when the PS3 market has become big enough, you can start offering some kind of online ordering system with different options.
It could happen, but I don't know. It highly depends on cost, but I'm starting to see how the internal WiFi and Memory Card reader might become an irrelevant cost (e.g. less than $10 combined), and since the PS3 is always going to have a HDD and 60GB becomes cheap, then why not.